Regeneration reaction

Gaseous Effluents. Twenty percent of the carbon disulfide used in xanthation is converted into hydrogen sulfide (or equivalents) by the regeneration reactions. Ninety to 95% of this hydrogen sulfide is recoverable by scmbbers that yield sodium hydrogen sulfide for the tanning or pulp industries, or for conversion back to sulfur. Up to 60% of the carbon disulfide is recyclable by condensation from rich streams, but costly carbon-bed... 

In addition to the Hquid-phase -butyl nitrite (BN) process, UBE Industries has estabHshed an industrial gas-phase process using methyl nitrite (50—52). The oudine of the process is described in Eigure 4 (52). This gas-phase process is operated under lower reaction pressure (at atmospheric pressure up to 490 kPa = 71 psi) and is more economical than the Hquid-phase process because of the foUowing reasons owing to the low pressure operation, the consumption of electricity is largely reduced (—60%) dimethyl oxalate (DMO) formation and the methyl nitrite (MN) regeneration reaction are mn... 

Reactions for Hydrogen Cation-Exchanger Resins -Regeneration Reactions... 

The formation of many polymer molecules on one active center is due to regeneration reactions, e.g. after the spontaneous transfer according to the scheme ... 

The fluidized reactor can be a bubbling fluidized type or a fast fluidized type, depending on the gas velocity and the reactivity of the sorbents. We adopted a fast fluidized bed type reactor for carbonation and regeneration reactions in order to identify the chemical characteristics of sorbents in a fast fluidized reactor of 0.025 m i.d. 

The reaction of eq. 16.9 will regenerate the antioxidant Arj-OH at the expense of the antioxidant At2-OH. Despite the fact that such regeneration reactions are not simple electron transfer reactions, the rate of reactions like that of eq. 16.9 has been correlated with the E values for the respective Ar-0. Thermodynamic and kinetic effects have not been clearly separated for such hierarchies, but for a number of flavonoids the following pecking order was established in dimethyl formamid (DMF) by a combination of electrolysis for generating the a-tocopherol and the flavonoid phenoxyl radicals and electron spin resonance (ESR) spectroscopy for detection of these radicals (Jorgensen et al, 1999) ... 

The rate of consumption of initiator should therefore be constant (i.e., of zero order) under given conditions. This deduction applies regardless of whether or not inhibitor radicals may undergo regeneration (reaction 63). It emphasizes again that the observation of a well-defined induction period of duration proportional to the amount of inhibitor initially present offers no assurance of a simple stoichiometric ratio between radicals stopped and inhibitor consumed. It will be observed that the rate of consumption of inhibitor, and therefore the length of the induction period for a given amount of inhibitor, depends exclusively on Ri if 2 = 0 if it depends also... 

Another successful C02 absorbent utilizing chemical interaction has been potassium carbonate used in the "hot carbonate process." The C02 absorption and absorbent regeneration occur at about the same temperature of 225°F in this process. C02 absorption occurs at high pressure and the sorbent regeneration occurs due to lowering of pressure with steam stripping. The absorption/regeneration reactions are represented as... 

Cyclic chain termination by antioxidants. Oxidation of some substances, such as alcohols or aliphatic amines, gives rise to peroxyl radicals of multiple (oxidative and reductive) activity (see Chapters 7 and 9). In the systems containing such substances, antioxidants are regenerated in the reactions of chain termination. In other words, chain termination occurs as a catalytic cyclic process. The number of chain termination events depends on the proportion between the rates of inhibitor consumption and regeneration reactions. Multiple chain termination may take place, for instance, in polymers. Inhibitors of multiple chain termination are aromatic amines, nitroxyl radicals, and variable-valence metal compounds. 

Enzymatic cofactor regeneration can be subdivided into two categories the enzyme-coupled approach, where two different enzymes are used (one for the production reaction, and one for the regeneration reaction) and the substrate-coupled approach, where one and the same enzyme is used for both production and regeneration (E = E2). The most convenient and commonly used enzymatic regeneration systems are summarized in Table 43.1. 

The AG molecule is converted to a strong acid (AH) upon absorption of a photon and the rate of this reaction is fast, with the extent of reaction being governed by the quantum effeciency of the particular acid generator and flux. The acid proton affects the desired deprotection reaction (4) with a finite rate constant. This rate is a function of the acid concentration, [H4-], the temperature and most importantly, the diffusion rate of the acid in the polymer matrix. The diffusion rate in turn, depends on the temperature and the polarity of the polymer matirx. At room temperature, the rate of this reaction is typically slow and it is generally necessary to heat the film to well above room temperature to increase reaction rates and/or diffusion to acceptable levels. The acid (H+) is regenerated (reaction 4) and continues to be available for subsequent reaction, hence the amplification nature of the system. 

The reaction can be controlled in an aqueous medium via pH and the use of a catalyst [91]. While the material hydrogen capacity can be high and the hydrogen release kinetics fast, the borohydride regeneration reaction must take place off-board. Regeneration energy requirements, cost and life-cycle impacts are key issues... 

The kinetics should be favorable (the regeneration should be fast and the regeneration reaction should be selective, thus requiring a suitable catalyst)... 

When electrochemical regeneration is nsed, the regeneration reaction equation is ... 

A regeneration reaction for NADH that may be used is the conversion of pyravate with a NADH-dependent lactate dehydrogenase (LDH) ... 

There are maty other examples of cofactor regeneration reactions and/or of reactions which may be performed in an enzyme membrane reactor. An important example is the regeneration of NADH by formate dehydrogenase (FDH), starting with formate (Wichmaim et al, 1981). The advantage of this reaction is that it is irreversible because carbon dioxide is hberated, while formate is a relatively cheap electron donor. 

In general, syntheses with isolated enzymes can be performed with higher selectivity and space-time yield than with whole cells, but they require in any case the coupling of coenzyme regenerating reactions. 

Catalytic reactions in electrochemistry — When the product of an electrochemical reduction reaction is regenerated by a chemical reoxidation, or when the product of an electrochemical oxidation is regenerated by a re-reduction, the regeneration reaction is called a catalytic reaction. For thermodynamic reasons the chemical oxidant (or the reductant) has to be electro-chemically irreversible in the potential range where the catalyst is electroactive. The reduction of Ti(IV) in the presence of hydroxylamine is an example for an oxidative regeneration [i, ii] ... 

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